1. Field of the Invention
The present invention relates to a semiconductor element drive device, a power conversion device having the semiconductor element drive device, a motor drive device, a semiconductor element drive method, a power conversion method, and a motor drive method.
2. Description of the Related Art
In a power conversion device in which high- and low-voltage side semiconductor elements are series-connected between main power supply terminals to form high- and low-voltage side arms, the high-voltage side semiconductor element is driven at a floating potential. Therefore, a drive circuit for the high-voltage side semiconductor element uses an insulated power supply. Further, a level shift circuit is necessary because a low-voltage side circuits transmits a drive signal to a high-voltage side circuit. The level shift circuit generally includes a pulse generation circuit and two nMOS-FETs. The pulse generation circuit generates a set pulse and reset pulse from the drive signal. The generated set pulse and reset pulse become gate inputs for the nMOS-FETs. It is demanded that this type of power conversion device exhibit, for instance, high withstand voltage, low loss, and high reliability.
In the power conversion device, the potential of a connection point between the low- and high-voltage side semiconductor elements suddenly changes from a ground potential of the low-voltage side semiconductor element to a main power supply voltage. In this instance, a parasitic capacitance exists between a drain and a source of the nMOS-FETs, which constitute the level shift circuit. Therefore, a current simultaneously flows to the two nMOS-FETs, which constitute the level shift circuit, due to a drastic potential change (dV/dt=great). The flow of such a current may transmit a wrong signal to a high-voltage side control circuit, thereby causing the high-voltage side semiconductor element to erroneously turn ON/OFF.
JP-A-1997-172366 and JP-A-2005-304113 call a drastic potential change at a series connection point a self-excited or separately-excited dV/dt, and disclose measures for preventing the level shift circuit from malfunctioning due to the self-excited or separately-excited dV/dt. More specifically, JP-A-1997-172366 avoids malfunction by providing the high-voltage side control circuit with a filter circuit, whereas JP-A-2005-304113 integrates the difference between a set signal and a reset signal and transmits a control signal to avoid malfunction.